The present invention relates to a reciprocating pump for inducting and discharging fluid by means of a reciprocating member, such as a piston, a plunger, or the like, and, in particular, to a reciprocating pump provided with a malfunction-detector for detecting malfunctions such as an induction failure and a failure to discharge a fluid under pressure to a destination.
A conventional reciprocating pump employed for the lubrication of a small air-cooled, two-stroke cycle gasoline engine (hereinafter referred to simply as an engine), which is suitable for use as a power source for a portable power working machine such as a chain saw, is shown in FIG. 3. The pump 2 includes a main body 60 having a cylinder portion 65 that is provided with an induction port 66 and a discharge port 67. The discharge port 67 is opened and closed by a ball valve 75. One end of a plunger rod 71 is affixed, such as by press-fitting, to a main plunger body 72 of a reciprocating member 70. The other end of the plunger rod is slidably received in the cylinder portion 65. A solenoid 80 attached to one end portion (on the right side in the drawing) of the main body 60 drives the reciprocating member 70. A delivery passageway member 90 is threaded into the other end portion (on the left side in the drawing) of the main body 60.
The ball valve 75 is normally urged in a direction to close the discharge port 67 by means of a coil spring 74, which is interposed between the ball valve 75 and the delivery passageway member 90. The reciprocating member 70 is normally urged toward the right side of the drawing by means of a coil spring 78 which is interposed between the cylinder portion 65 and the main plunger body 72.
The solenoid 80 is secured between the main body 60 and a retainer sleeve 84, which is threaded onto the outer circumferential wall of one end of the main body 60. A cupshaped cover 85 fits over and is affixed to the outer circumferential wall of the retainer sleeve 84.
The solenoid 80 is energized by current pulses supplied to it at a predetermined cycle from an outside power source (not shown) by electrical conductors (not shown) that pass through a hole 68 in the main body 60. When the solenoid 80 is switched to OFF from ON, the reciprocating member 70 is caused to move rightward in the drawing due to the urging force of the coil spring 78, thereby moving the plunger rod 71 in a direction to open the induction port 66. As a result, fluid (lubricating oil for the engine) is permitted to flow into a valve chamber 61 which is formed between the plunger rod 71 and the ball valve 75, and at the same time, a rear flange portion 73 of the main plunger body 72 engages and is stopped by the cover 85. FIG. 3 shows the state of the pump 2 when the solenoid 80 is OFF.
When the solenoid 80 is switched to ON, the reciprocating member 70 is caused to move leftward in the drawing due to the generation of magnetic force, thereby moving the plunger rod 71 in a direction to close the induction port 66, and at the same time, the fluid in the valve chamber 61 is pressurized so as to push the ball valve 75 open (leftward in the drawing). The flange portion 73 of the main plunger body 72 engages a plastic buffer plate 88 adhered to the right end face of the retainer sleeve 84. As a result, the discharge port 67 is opened, thus permitting the fluid in the valve chamber 61 to flow into the delivery passageway member 90.
When the pump 2 of FIG. 3 is installed on an engine, lubricating oil in an oil tank (not shown) is inducted through an oil strainer and an inlet pipe (not shown) into the valve chamber 61 from the induction port 66. The lubricating oil thus inducted into the valve chamber 61 is then pressurized and is discharged from the pump 2 through the discharging port 67, the ball valve 75, a delivery passageway 92 in the delivery passageway member 90, a check valve 95 disposed at the delivery port of the delivery passageway 92, and an oil delivery pipe (not shown) coupled with the delivery passageway member 90, to the destination, i.e., the moving parts of the engine.
Like any pump, the reciprocating pump described above may malfunction. For example, the induction side of the pump may become clogged so that the oil is no longer normally inducted, or air may be inducted with the oil due to a leak in the line leading to the pump from the supply tank. Also, the pipe leading from the discharge side of the pump may become clogged, thereby making it impossible to feed the oil to the destination thereof. In the event of a malfunction of the pump, it is desirable to stop the engine to avoid seizure or to provide an alarm, warning of the malfunction.
It is conventional to attach a pressure sensor to the reciprocating pump so as to detect a fluctuation of pressure at the delivery port. In this case, the aforementioned abnormalities in the operation of the pump can be detected based on an output (detection signal) emitted from the pressure sensor.
More specifically, as shown in FIG. 3, a take-off port 97 is provided on the delivery passageway member 90 so as to provide via a rigid pipe 98, for instance, a quantity of oil present at the delivery port (a delivery pressure) to a pressure sensor 100, which detects fluctuations of pressure at the delivery port. Suitable pressure sensors 100 include transducer type sensors, which are designed to generate an electric signal after converting the delivery pressure of oil into another kind of physical quantity (such as the magnitude of displacement) by making use of a diaphragm or the like. Transducer-type sensors include those having a strain gage adhered to a diaphragm, those having a coil and a core symmetrically arranged on both sides of a magnetic diaphragm so as to constitute an equilibrium magnetic circuit, and those in which a conductive diaphragm and an electrode are arranged to face each other so as to constitute a pair of capacitors. The foregoing types are available commercially.
In previously used types of pressure sensors, the output of the pressure sensor 100 changes synchronously with the ON/OFF operation (the discharging and inducting operation by the reciprocating member 70) of the solenoid 80 as shown in FIGS. 4(A) to 4(C). When the oil is normally supplied without the aforementioned abnormalities, the output of the pressure sensor 100 becomes wavy, as shown in FIG. 4(A); when the oil is cut off, the sensing of a change in output from that of the normal operation slightly lags in time behind (due to the entrainment of air) and at the same time, the amplitude of output is slightly reduced, as shown in FIG. 4(B); and when the clogging of oil occurs on the delivery side of the pump, the output of the pressure sensor 100 is greatly increased, as shown in FIG. 4(C). Therefore, it becomes possible, through the processing of the output of the pressure sensor 100, to detect the type of abnormality in the operation of the pump.
The pressure sensors which are generally available commercially, such as those mentioned above, are somewhat expensive for use in detecting abnormalities, such as the cutoff of oil from the pump intake or the clogging of oil on the delivery side, of a reciprocating pump employed for the lubrication of the engine of a portable working machine such as a chain saw. In addition to the relatively high cost, it is also required in the case of the aforementioned pressure sensors to introduce a fluid such as oil directly into the pressure sensor, thereby raising a problem of the space for mounting the aforementioned pressure sensors on the reciprocating pump.
The present invention has been made in response to the aforementioned needs. In particular, it is an object of the present invention to provide in a reciprocating pump a detector that is capable of reliably detecting abnormalities in the inducting and discharging of fluid, such as the cut-off of oil from the pump intake or the clogging of oil on the delivery side of the pump, by a detector that is inexpensive and relatively simple in structure.
With a view to attaining the aforementioned object, the present invention provides a reciprocating pump having a chamber, a reciprocating member arranged to induct a fluid into the chamber and discharge the fluid from the chamber to a delivery side of the pump, and a piezoelectric element attached to the pump and arranged to detect pressure fluctuations on the delivery side of the pump so as to sense any abnormality in the inducting and discharging of fluid.
In a preferred embodiment, the piezoelectric element is of tubular configuration and is fitted on an outer wall of a delivery passageway member which constitutes the delivery side of the pump. An insulating member may be interposed between the piezoelectric element and the delivery passageway member.
In advantageous arrangements, a tubular piezoelectric element is engaged between a flange portion of the delivery passageway member and a main body of the pump. An insulating member may be interposed between the piezoelectric element and the delivery passageway member, and another insulating member may be interposed between the piezoelectric element and the main body.
The reciprocating pump may be of a type in which the chamber is defined by a cylinder portion of the main body. The cylinder portion has an induction port and a discharge port. The discharge port is opened and closed by a valve and when opened discharges the fluid to the output side, such as the aforementioned delivery passageway member. The reciprocating member is received for reciprocating movement in the chamber of the cylinder portion to thereby induct the fluid into the chamber through the induction port and discharge the fluid from the discharge port to the delivery passageway member. A solenoid drives the reciprocating member.
The reciprocating pump according to the present invention is well suited for use as an oil pump to supply a lubricating oil to an engine.
In the operation of a reciprocating pump of the present invention which is constructed as described above, the delivery passageway member expands and contracts due to a fluctuation of pressure of the fluid present on the delivery side of the reciprocating pump. The forces resulting from the deformation of the delivery passageway member are transmitted via the insulating member to the piezoelectric element. As a result, the piezoelectric element expands or contracts, and hence the output (detected signals) from the piezoelectric element change, depending on the aforementioned fluctuation of pressure.
The output from the piezoelectric element is essentially identical with the output of the aforementioned previously used pressure sensors, so that when the output from the piezoelectric element is processed by means of a computer, the type of abnormality in the operation of the pump, such as a cut-off of the supply of oil to the pump intake or the clogging of oil on the discharge side of the pump, can be automatically detected.
Piezoelectric elements of a tubular configuration are available commercially at prices considerably less than those of the aforementioned pressure sensors previously used with engine-lubricating pumps. Additionally, it is not necessary to introduce oil directly into the piezoelectric element. Moreover, the tubular piezoelectric element can be easily fitted on the outer wall of the delivery passageway member and supported between the delivery passageway member and the main body, thereby considerably simplifying the attachment of the piezoelectric element to the pump.
As described above, it is possible according to the present invention to reliably detect abnormalities in the inducting and discharging of fluid such as the cut-off of oil from the supply tank or the clogging of oil on the delivery side by making use of an inexpensive piezoelectric element, which is also relatively simple in structure.